The invention relates generally to the “active implantable medical devices” field as defined by Directive 90/385/EEC of 20 Jun. 1990 the Council of the European Communities. The invention more specifically relates to a detection and/or stimulation microlead intended to be implanted in venous, arterial or lymphatic networks, and to deliver an electrical pulse and/or to detect an electrical activity. Such a lead can be used in cardiology and, for example, can be implanted in the coronary sinus vein to stimulate a left or right cavity of the heart. Microleads are also useful in many other medical applications. For example, microleads can be used whenever there is a venous, arterial or even lymphatic network, including the venous or arterial cerebral network. Electrical stimulation led to major advances in neurology in the field of neuromodulation, a technique which includes stimulating target areas of the brain for the treatment of disorders such as Parkinson's disease, epilepsy and other neurological diseases. Such a technique can advantageously provide a less invasive approach.
A continuing challenge in many microlead applications is to reach areas which are relatively inaccessible due to small size constraints. Some stimulation “microleads” are therefore of very small diameter but are also extremely robust to ensure the long-term biostability.
The size of some current implantable leads is on the order of 4 to 6 French (1.33 to 2 mm). It would be desirable to reduce the diameter to less than 2 French (0.66 mm). Such a size of microlead would reach very small veinlets, inaccessible today with some types of larger devices. It is challenging to provide microleads of such small size which are also able to easily navigate through the venous arterial or lymphatic networks with sufficient flexibility to be introduced into vessel networks with high tortuosity, anastomosis, etc. The reduction in lead diameter increases microlead technological complexity, imposes technical constraints, and generates technical risks.
Some leads include a microcable having a central conductor for connection to an electrical generator. The conductor may be coated with an electrically insulating sheath. One or more sensing/pacing electrodes may be electrically connected to the central conductor, and are intended to come into contact with the wall of the target vessel.
One technique for producing electrodes of such leads is described in EP 2455131 A1 and its US counterpart US2012/0130464 (Sorin CRM SAS). This technique includes locally stripping the insulation to expose the microcable in one or more points. The stripped points together form a network of electrodes connected in series to provide the stimulation points and thus ensure multizone dissemination of the stimulation energy delivered by the implant. The same document also proposes an alternative embodiment in which the working portion of the microlead is provided by successively and alternately threading on the microcable insulating tubes and short conductive electrodes of platinum-iridium. The insulating tubes, made for example of polyurethane, are affixed to the microcable and the platinum-iridium electrodes are crimped directly to the microcable. Another technique includes applying a coating of the microcable of insulating polyurethane adhesive, leaving some uncoated conductive surfaces.
With these techniques, which include the exposure of microcable (removal of the insulating surfaces or surfaces left in reserve), it is desirable to provide a conductive coating, such as an alloy of titanium nitride or a carbon deposit such as Carbofilm by a cathode sputtering technique such as described in particular in U.S. Pat. No. 5,370,684 A and U.S. Pat. No. 5,387,247 (Sorin Biomedica SpA), to protect from corrosion the exposed cable. The conductive coating may be made of an alloy such as MP35N (35% Ni, 35% Co, 20% Cr and 10% Mo). However, such a material is relatively sensitive to electrocorrosion, a corrosion phenomenon accentuated by the current flow in the polar regions (electrodes) and by contact with surrounding body fluids (blood, etc.).
In some applications it may be desirable to avoid any risk of infusion of corporeal fluids to the microcable. The microcable may thus be completely isolated from any contact with the environment of the microlead. This can be provided by an additional conductive coating of titanium nitride NiTi or carbon on the electrode areas or crimping platinum-iridium rings (noble material, resistant to corrosion) on the microcable.
Long life duration is a key parameter which must be taken into account when designing a stimulation microlead. Indeed, the heart beats and movement of organs can induce significant bending strains. In particular, a stimulation microlead by the venous system may be locally deformed under curvatures much higher than those experienced by a conventional lead, since it must follow the deformation of the veins.
French patent application FR 12 54548 of May, 16, 2012, titled “Structure of electrode for a detection/stimulation monopolar microlead intended to be implanted in a cardiac or brain vessel” proposes to produce the detection/stimulation electrode in the form of a metal ring crimped onto the microcable. The inner face of the ring is in mechanical and electrical connection with the microcable surface in at least one perforation region of the sheath. However, at the periphery, the inner face of the ring is in mechanical connection with the surface of the sheath. In other words, insulating material of the sheath is positioned between the microcable and the ring in regions on both sides the perforation area of the sheath. An advantage of such electrodes is that they do not require stripping the microcable to electrically connect to the central conductor. Such electrodes also do not require a special conductive coating or NiTi carbon.
In some applications, however, it is desirable to have a multipolar lead. A multipolar lead can provide for bipolar stimulation by delivering pulses between two electrodes located at the end of a lead, or between two electrodes of a right ventricular lead. This stands in contrast to stimulation between an electrode (or a series of electrodes) and the housing of the generator, such as with many monopolar lead.
Another advantage of the multipolar leads is the possibility to implement an “electronic repositioning.” This feature allows a surgeon to select, from the various electrodes present on the lead, the electrode which provides the best compromise between prevention of phrenic nerve stimulation, electrical efficiency and hemodynamic effectiveness. Such a multiple electrode lead is in particular described in EP 1983881 A1 and its US counterpart US2008/0177343 (Sorin CRM S.A.S.). In this method, it is possible to direct or redirect the electric field between the different electrodes arranged along the pacing lead of the left cavity and/or with the electrodes of the pacing lead of the right ventricle. This technology allows managing micro-displacements and changes in the hemodynamic behavior (reverse modelling) simply by reprogramming the generator by telemetry through the skin, without heavy reoperation. U.S. 2008/0114230 A1 and U.S. Pat. No. 7,364,479 B1 describe exemplary electrode supporting structures for such a multipolar lead.
In the case of a multipolar lead, the presence of a plurality of conductors (typically three conductors) disposed along the lead body renders conventional crimping of a ring-shaped electrode as impractical, because such conventional crimping would likely indiscriminately perforate the conductors of the lead.